This invention relates to steel casting containing Niobium.
This invention further relates to chromium-molybdenum-vanadium (Cr—Mo—V) steel castings containing niobium, for use in steam turbine casing or valve casing applications.
To improve the mechanical properties and weldability of steels, various alloying elements such as Ti, Nb, Mo, W, B etc. have been added to low and high alloy steels. Ti and Nb are added as carbide formers and strengthen the alloy steels by forming fine matrix carbides which interact with dislocations and precipitate at subgrain boundaries thus reducing the secondary creep rate.
Presently, Cr—Mo—V based steel castings are being used for turbine casing and valve casing applications up to around 540° C. Due to increase in power demand and limitation on CO2 emission, there is increasing demand for higher efficiency and output of the steam turbines. It is possible, by increasing the temperature and pressure of the turbine without much increase in cost.